Formula
Round half up: look at the first dropped digit; 5–9 rounds up, 0–4 rounds downNearest 10ⁿ: shift, round to a whole number, shift back How it works
Rounding replaces a number with a simpler one that is close to it. To round to two decimal places, look at the third decimal digit: if it is 5 or more, increase the second digit by one; otherwise leave it. So 3.14159 rounds to 3.14 and 2.675 rounds to 2.68.
Negative “decimal places” round to the left of the decimal point: −1 rounds to the nearest ten, −2 to the nearest hundred, and so on. 1,849 rounded to the nearest hundred is 1,800.
The standard school rule always rounds a 5 up (away from zero), which slightly biases totals upward when many numbers are rounded. Banker’s rounding avoids that bias by sending exact halves to the nearest even digit, so 2.5 becomes 2 and 3.5 becomes 4. Ceiling, floor and truncate always move in one direction, which is useful for things like “how many boxes do I need?”.
Frequently asked questions
Why does my spreadsheet round 2.675 to 2.67?
Computers store decimals in binary, so 2.675 is really 2.67499999… This calculator removes that tiny error before rounding, giving the answer you would get by hand: 2.68.
How do negative numbers round?
With the standard rule, halves round away from zero, so −2.5 becomes −3. Floor always goes down (−2.5 → −3) and ceiling always goes up (−2.5 → −2).
Is rounding the same as significant figures?
Not quite. Rounding to decimal places fixes the position of the last digit, while significant figures fix how many meaningful digits are kept. Use the significant figures calculator for the latter.